1. Field of the Invention
This invention relates to the extraction and purification of tungsten values from aqueous alkali metal tungstate solutions. More particularly it relates to a two component extractant solution useful for extracting and purifying tungsten values from an aqueous caustic solution.
2. Prior Art
Extraction of tungsten by amines has been known for a number of years as reported by Coleman, C. F., et al., "Amines as Extractants," Nuclear Science and Engineering, Vol. 17, 274-286, 1963 and C. R. Kurtak in U.S. Pat. No. 3,158,438, 1964 describes an integrated solvent extraction process using an amine. A long chain aliphatic alcohol is used as a phase conditioner (or solubilizer). P. Coad in U.S. Pat. No. 3,804,941 describes tungsten recovery from an aqueous alkaline brines solution using quaternary amine. Tungsten recovery from low grade concentrates containing low concentration of tungsten using a primary amine and a quaternary amine-- is reported in Investigation 6845, U.S. Department of the Interior. More recently a tricaprylyl amine, tributyl phosphate and kerosene system has been used. A preferred kerosene is a material sold under the trade name Kermac 470 B by Kerr-McGee. In the above system tributyl phosphate is essential for the amine-tungsten-complex to remain soluble in the organic extractant solution. Without tributyl phosphate the complex is insoluble and the system cannot be operated. Generally a solution containing from about 10 to about 14 percent by volume of the tricaprylyl amine, from about 10 to about 14 percent by volume of tributyl phosphate and the balance kerosene is used.
While the tricaprylyl amine-tributyl phosphate-kerosene system provides satisfactory recovery of tungsten it does have some disadvantages. In addition to the necessity of using tributyl phosphate to provide solubility for the amine-tungsten complex, sodium is extracted along with the tungsten. In addition, tributyl phosphate hydrolyzes to produce di-n-butyl phosphoric acid and mono-n-butyl phosphoric acid. These acids extract cationic impurities. It is also necessary in the above extraction system to add heat.
It is believed, therefore, that a solvent system that does not use tributyl phosphate, has a higher throughput capability can be operated without addition heat and provides a product relatively free of sodium is an advancement in the art.